The critical role of thin films in modem electronic and photonic devices is well established. Useful films include a wide range of metals, semiconductors and insulators, in simple, multicomponent, and multilayer form. An impressive number of established film deposition methods and materials are amply described in the "bible" of the field, "Handbook of Deposition Technologies for Films and Coatings", 1994, edited by Rointan F. Bunshah.
However, one intriguing class of thin film has largely eluded efforts at economic and efficient synthesis up to the present time. This is the class of "doped" or "host-guest" film in which organic molecule guests are incorporated in hard, ceramic, inorganic hosts. Doping is an important way of modifying the properties of materials; examples are transistors in electronics, and lasers in optics. The lure of doping hard coatings with complex organic molecules is particularly strong. Because of their unusual and varied electronic structure, and their nearly infinite variety of chemical properties, organic molecule dopants raise many fascinating possibilities for thin film applications that cannot be realized in other ways. The ability to make these doped films opens the way to nearly limitless synthetic combinations of organic and inorganic chemistry with application to nonlinear optical-electronic integrated circuits, thin film lasers, chemical sensors, and novel decorative films.
There have been several approaches to doping thin films with complex organics. Dye molecules can be dissolved in liquid plastics or polymers which are then painted on substrates and solidified. However, this is a slow process, not compatible with high throughput modern semiconductor, vapor deposition technology. Of equal importance, the properties of plastics or polymers may not be as desirable in a host as those of hard ceramics such as oxides; photoinduced reaction of dye and matrix is one possible side effect, and thermal degradation is another. Luminescent organic molecules have indeed been trapped in low melting glasses such as boric acid, and in sol-gel oxide matrices, but these materials also have limitations. The sol-gel process involves multiple, time consuming steps, employs solvents hazardous to health, and lends itself poorly to vapor-based integrated circuit manufacture.
The majority of established deposition processes fall into two categories, chemical vapor deposition (CVD) and physical vapor deposition (PVD); both have disadvantages. In CVD, the substrate must be kept hot in order to reactively deposit an oxide host while the organic guest co-deposits; thermally fragile organics are unlikely to survive in CVD. In PVD, high vacuum requirements limit throughput and impede continuous operation; organics are not regarded as compatible with high vacuum systems, and some PVD methods involve plasmas that are detrimental to organic molecule stability. It is difficult to envision either a CVD or PVD approach to organic-ceramic host-guest films that is simple, reliable, fast and versatile.
It is therefore advantageous to have a method and apparatus for depositing organic-ceramic host-guest films based on vapor deposition. It is similarly advantageous to have a method and apparatus of the foregoing type capable of not only trapping a variety of organic molecules in ceramic host, but doing so at an economically attractive rate over substantial areas and on useful substrates. The present method and apparatus is drawn towards such an invention.